Beef Stroganoff

Yield:	6 Servings
Categories:	Low Fat, Beef

1 1/2	lb	Lean beef; round or flank steak
1/2	ts	Salt
1/4	ts	Pepper
2	tb	Diet margarine
1/2	lb	Fresh mushrooms; sliced
1/2	c	Onion; chopped
1	c	Beef broth
1	ts	Mustard powder
1		Whole bay leaf
2	tb	Tomato paste
1	tb	Flour
2	tb	Water
3/4	c	Plain nonfat yogurt